It is often desirable to accelerate an object to a high speed. For example, in order to launch an object into orbit around the Earth or to send an object into interplanetary space, the object must accelerated sufficiently to overcome the force of Earth's gravity. The velocity at which an object must travel to escape the gravitational pull of a body is referred to as “escape velocity.” For the Earth, escape velocity is about 25,000 mph. In order to place an object into orbit around the Earth, the object must be accelerated so that the pull of the Earth's gravity is balanced by the inertia of the object. Orbital velocity varies with the distance of the object from the Earth. At a typical space shuttle orbital altitude of 200 miles, orbital velocity is about 17,000 mph. It may also be desirable to accelerate an object to a lower, but still substantial speed, greater than Mach 3, for example, prior to launching the object into space or for other, unrelated reasons.
To date, the only practicable mechanism for accelerating an object to orbital or escape velocity has been the rocket. Rockets are expensive. The cost of many rocket launches is in the 50 to 100 million dollar range. The National Aeronautics and Space Administration (NASA) estimates that a typical space shuttle launch costs over 450 million dollars. Rocket engines are also dangerous, as shown by the numerous failures during the history of rocketry. Rockets may also be difficult to control once ignited. While liquid fueled rockets offer users some ability to control thrust, more powerful solid fuel rocket engines generally burn until the fuel source is depleted, with little opportunity to vary thrust and/or abort a launch. The cost and danger of using rocket engines has thus limited the number and type of outer space-related projects that are undertaken.
Beneficially, rockets carry their own source of oxygen and can thus burn and provide thrust under conditions where other propulsion systems, such as jet engines, can not operate, such as in the near vacuum of outer space. However, jet engines are routinely used at altitudes of 50,000 feet and higher. It has therefore been suggested that a rocket be carried to such an altitude by a large jet aircraft and launched into orbit from that altitude. Jet fuel rather than rocket fuel is thus used to impart an initial velocity and altitude to the object. While this method provides some benefits, a substantial amount of rocket fuel is still required to lift the object from 50,000 feet to a desired orbital altitude. In addition, there are other costs associated with operating and maintaining aircraft capable of carrying a rocket to a desired altitude. Thus the reduction in rocket-related costs associated with launching from a high altitude is often offset by the cost of lifting the rocket to that high altitude in the first place. Such systems might be economically feasible if used very frequently, daily, for example; however the demand for such frequent launches does not as yet appear to exist.
Other, more exotic devices for placing objects into orbit have also been suggested, one of which is the space tether. A space tether comprises a massive anchor that orbits around the Earth and an extremely long tether extending therefrom. The anchor rotates as it orbits, and the tether projects radially from the rotating anchor and is held taut by centrifugal force. The free end of the tether traces out a generally circular path. The anchor is positioned so that the circular path intersects the Earth's atmosphere, and the free end of the tether periodically moves through Earth's atmosphere. Objects can be placed into outer space using this system by accelerating them to the speed of the tether through the atmosphere, generally about Mach 12, attaching them to the tether, and allowing the inertia of the rotating tether to carry them into space where they are released.
Tethers 250 to 1000 miles long can be made using produces available today. Information on space tethers can be found in the documents entitled “AIAA-99-4802 Hypersonic Airplane Space Tether Orbital Launch (HASTOL) System: Interim Study Results” by Bogar, et. al., presented at the 9th International Space Planes and Hypersonic Systems and Technologies Conference 1-5 Nov. 1999, Norfolk, Va, which is hereby incorporated herein by reference. A significant problem with using such tethers, however, is the difficulty involved in accelerating objects to the Mach 12 or so required to match the speed of the tether.
It is therefore desirable to provide a method and system for accelerating an object to a high velocity in an efficient manner.